This application generally relates to optical systems, and more particularly to an all-reflective wide-field-of-view telescope with beneficial distortion correction.
Many wide-field-of-view (WFOV) optical systems, whether reflective or refractive, are of the inverse-telephoto family. This generally means that there is considerable negative optical power in the optical elements at the front of the optical system and considerable positive optical power in the optical elements at the rear of the optical system. In contrast to this, the family of telephoto optical forms has considerable positive optical power in front and considerable negative optical power at the rear. Examples of inverse-telephoto optical system are described, for instance, in U.S. Patent Application Publication No. 2008/0266687, herein incorporated by reference in its entirety. These optical systems may be characterized, for example, as having a large negative powered first optical element, or the so-called “fish-eye” configuration.
Typically, these systems have noticeable negative (or barrel) distortion, i.e., where the focal length at the edge of the field of view (FOV) is shorter than at the FOV center. This gives rise to image compression at the FOV edge. When used in an airborne or space-borne sensing application, the shorter focal length at the FOV edge combines with the longer range at the FOV edges to greatly increase the ground sample distance (GSD). This is generally detrimental to the spatial resolution of optical systems at the FOV edges.